Add keystore2 to PLATFORM_PACKAGES

Add keystore 2 to the PLATFORM_PACKAGES in anticipation for the Keystore
2.0 migration. This builds and installs keystore2 on the device, but it
does not get started yet. Staring keystore2 is currently controlled with
the platform property ro.android.security.keystore2.enable=true.

Bug: 171305684
Test: keystore2 builds and is present on the device but does not start
      unconditionally.
Change-Id: Id92cb2aa38022516067853d89d6c3210db1100a8